Omitted value
= Omitted value
{title2=$w\notin f(D)$}
An <omitted value> of a <function> $f:D\to Y$ is a point $w\in Y$ outside its <image>: the equation $f(z)=w$ has no solution in $D$. Both $D$ and $Y$ matter. The <complex exponential function> on the <complex plane> has one <omitted value> in $\mathbb C$, namely zero, and two <omitted values> when regarded as a map into the <Riemann sphere>, namely zero and infinity. Restricting $D$ can create additional <omitted values>.